Most modern vehicles may be fitted with a brake booster which utilizes a vacuum chamber to increase the braking force supplied from the brake pedal to the brake master cylinder. The brake booster prevents the brake pedal from feeling heavy to the driver.
The brake booster may require a source of vacuum pressure however in order to operate, which, in naturally aspirated engines, is often delivered exclusively by the inlet manifold of a vehicle. Under some circumstances, the vacuum supplied by the inlet manifold may be insufficient. This may be due to a large amount of torque being demanded from the engine, either for mechanical drive or to power auxiliary electrical systems of the vehicle. In this case, the inlet throttle may be fully open and thus, an inlet manifold vacuum may be low.
In order to maintain the brake booster vacuum under these conditions, an additional vacuum source must be used, such as a super aspirator. A super aspirator often takes the form of a venture duct connected between the intake duct and an inlet manifold across the inlet throttle. The pressure difference across the throttle drives a flow through the venture allowing for a lower pressure to be achieved within the venture. This may in turn be used to provide a lower pressure in the brake booster vacuum chamber compared to the inlet manifold pressure.
In some cases, sufficient pressure difference may not be available for a venture duct to operate effectively, and a separate pump may then be required to provide a vacuum source. Whatever form the vacuum source takes, a shut-off valve is often added which may be opened only when insufficient vacuum pressure is detected within the brake booster and/or inlet manifold. The shut-off valve is typically controlled by the engine's power-train control module and is normally in a closed position unless activated.
However, the inventors herein have recognized potential issues with such systems. As one example, in the case that the super aspirator itself or the electronic shut-off valve fails, sufficient vacuum pressure may not be available within the brake booster and the brake pedal may begin to feel heavy. A heavy brake pedal provides a less comfortable driving experience and may lead drivers to believe that braking performance may be impaired. Thus, it may be desirable to limit faults of this kind.
In one example, the issues described above may be addressed by a method for detecting a fault within a brake booster system of a vehicle, the vehicle comprising an inlet manifold for an engine, the inlet manifold providing a first source of vacuum for the brake booster system, the vehicle further comprising a second source of vacuum for the brake booster system, wherein the method comprises: measuring the presence of a brake booster chamber and the pressure in the inlet manifold when the secondary vacuum source is instructed to be active; comparing the measured brake booster chamber and inlet manifold pressures; and determining whether the secondary vacuum source is faulty. The method may further comprise restricting the use of a first electrical system which draws power from the engine in the case of a fault so as to reduce and/or maintain the pressure of the inlet manifold. In this way, it may be possible for the brake booster system of the present disclosure to maintain the pressure of the brake system such that a user such as the driver of a vehicle may not experience an unnecessarily heavy or difficult to engage brake pedal.
As one example, a method for detecting a fault within a brake booster system of a vehicle engine is provided. The engine may include an inlet manifold comprising a first source of vacuum and a second source of vacuum. The method for detecting a fault within the brake booster system may comprise measuring the pressure of a brake booster chamber and the pressure in the inlet manifold, comparing the measured brake booster chamber and inlet manifold pressures, determining whether the secondary source of vacuum is faulty, and restricting the use of an electrical system which may draw power from the engine in the case of a fault. In this way, it may be possible to reduce and/or maintain the pressure within the inlet manifold to fall within a desirable pressure range. This may further allow for the brake pedal of the vehicle to maintain its resistance with respect to the amount of pressure necessary for a user such as a driver to apply to the brake pedal.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.